Determination of the Effect of Ketamine, Thiopental and Halothane on the Ocular Electroretinographic Examination of the Beagle Dog to Define Protocols to be Used in Dogs, Monkeys and Micropigs

Summary

A preliminary study performed on anesthetized beagle dogs permitted definition of a protocol for electrophysiological examinations. This first protocol included dark adaptation and specific stimulation of cones (red flashes) and rods (blue flashes).

As the less variable and therefore most interpretable values were latencies and not amplitudes, and as dark adaptation only increases amplitude, it was decided to perform further routine examinations without dark adaptation.

It was also decided not to evaluate systematically differential receptor function in further routine studies. Therefore, most of the records were obtained using only polychromatic light (white flashes).

A subsequent study was performed in order to compare the influence of different types of anesthetics on two of the main electroretinogram waves in the beagle dog and showed good homogeneity of values for each kind of anesthetic and a trend to variable increases in latencies depending on the anesthetic. It was found that results could be easily obtained in conscious dogs.

Consequently, it was decided to perform further examination without anesthesia in beagle dogs and, where possible, in other species such as micropigs. It is not possible to perform electroretinographic records in conscious animals for species such as primates. In this case, it was decided to anesthetize the animals, using ketamine, which was the drug which produced the least marked increase in the wave latencies in the beagle dog.

This survey is illustrated by records performed on normal eyes of beagle dogs, cynomolgus macaques and Yucatan micropigs and by some spontaneous or induced pathological changes.

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